Igniter and combustion apparatus



Aug. 28, 1956 c. E. SEGLEM 2,760,340

IGNITER AND COMBUSTION APPARATUS Filed Aug. 30, 1954 FUEL 23 GNITER TUBE OOOOOOOO Fig. l

Fig. 5

INVENTOR CLIFFORD E. SEGLEM BY efiwugm ATTORNEYS United States Patent IGNITER AND COMBUSTION APPARATUS Clifford E. Seglem, Pittsburgh, Pa., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application August 30, 1954, Serial No. 453,170

1 Claim. c1. 6039.82)

This invention relates to an igniter and more particularly to a heater plug and shield therefor for igniting fluid fuel in jet engines and gas turbines.

Jet engines and gas turbines are usually started by first actuating the moving power elements such as the compressor and the turbine by outside power means. This causes a blast of air to flow through the combustion chamber, which blast of air is usually at a pressure other than atmospheric. Both the high velocity of the blast of air and the diflference in pressure from atmospheric make the ignition of the fuel in such engines difl'icult.

Igniters which project a torch-like flame into the combustion chambers of jet engines and gas turbines have proven to be reliable means for igniting the main fuel in these combustion chambers under adverse conditions. However, most torch igniters operate at high pressures to ensure the projection of the flames into the combustion chambers which are already above atmospheric pressure. The high internal pressure of the igniter often results in a high rate of air and fuel flow therethrough, reducing the time of contact between the fuel and the oxidant to a minimum and inhibiting proper atomization or vaporization of the fuel, resulting in poor starting characteristics for the igniter.

Igniters are fired by spark plugs or by heater plugs. Most commercial heater plugs have either an exposed unshielded element or coil projecting into the fuel and air stream, or a cylindrical shield which completely surrounds the coil with no provision for utilization of any but the last few turns of the coil for ignition, since none of the fuel and air can come into good contact with the entire length of this type of shielded coil. The plugs with unshielded elements are cooled by the air and fuel stream and by the evaporation of fuel particles and must be operated at very high temperatures to ensure ignition. Once ignition occurs, the elements are no longer radiating to cool gases, but to hot flames instead; the element temperatures rise and the elements usually erode or melt.

It is an object of this invention to provide a new and improved heater plug for igniting a moving stream of fluid fuel and oxidant.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawings, which illustrate a preferred embodiment, and wherein:

Fig. 1 is a diagrammatic representation, mainly in section, of a combustion chamber for a gas turbine;

Fig. 2 is an enlarged elevational View of a portion of the igniter of Fig. 1;

Fig. 3 is a sectional view taken along line 33 of Fig. 2 showing details of the heater plug and shield of this invention;

Fig. 4 is a sectional view of the igniter tube and heater plug taken along line 4-4 of Fig. 3; and

Fig. 5 is a sectional view of the igniter tube and heater plug taken along line 5-5 of Fig. 3.

Referring to Fig. l of the drawing, generally designates an annular air passageway formed by walls 11 and has combustion apparatus indicated generally at 12 disposed therein between a turbine section represented by blade 13 and a compressor section represented by blade 14 of a turbo compressor unit for which the invention is particularly adapted. Air is supplied to the turbine compressor unit for passage therethrough and the combustion apparatus 12 is apertured for receiving air from the passageway while a fuel supply line 15 is provided to form a combustible mixture within the combustion apparatus. The igniter for the combustion chamber is made up of an igniter tube 16 extending through the outer wall 11 and has one end portion in communication with the combustion apparatus and its other end portion disposed exteriorly of the outer wall 11. Liquid fuel is supplied to the outer end portion of the tube by conduit 18 and air is supplied thereto by conduit 21 and pumping means 23. A heater coil element 22 is disposed in the igniter tube between the inlets of the fuel and air supply and the inner end portion of the tube and is connected with a source of electrical energy by wires 25 to supply the required heat for the coil. The igniter just described provides an independent combustible mixture which in passing over the heater element 22 is ignited and the flame produced thereby is directed into the primary combustible mixture in the main combustion chamber.

Referring now to Figs. 2, 3, 4 and 5, the heater plug 22 is shown in position in the igniter tube 16. The plug 22 comprises a base 31 which is adapted to fit in a cylindrical aperture in the wall of the igniter 16 and carries a heater element 32 formed of a core and a surrounding spiral of resistance wire. A shield 33 is secured on one end to the base 31 and partially encircles the heater element 32. The shield 33 has a narrow longitudinal slot 34 through one side of its wall, the slot 34 extending from the top edge toward the base a distance which is approximately equal to the inside diameter of the igniter tube 16, and has an aperture 35 diameterically opposite the slot 34 and of the same length. The slot 34 may range in width from to A the diameter of the shield 33, with a width of approximately the diameter being preferred, and the aperture 35 may range in width from 45 to 135 of the circumference of the shield 33, or from A to A, the diameter of the shield 33, with a width of approximately of the circumference of the shield 33, or /2 the diameter, preferred. The longitudinal center lines of the slot 34 and the aperture 35 are diametrically opposite each other.

As viewed in Figs. 2 and 4, the flow of the fuel and the air mixture through the igniter tube 16 is from the top, downward, and the shield 33 is positioned in the igniter tube 16 in the path of the fuel and air flow with the slot 34 upstream.

In operation, when the combustion chamber 12 is to be ignited, the power units, represented by blades 13 and 14, are rotated, sending a blast of air through the combustion chamber 12, and air under pressure is introduced into the igniter 16 by the pump 23 through the pipe 21. The heater element 32 of the heater plug 22 is energized and the resistance wire becomes hot.

A part of the air flowing through the igniter tube 16 is diverted by the shield 33 to flow around it on both sides. The flow of a gas around a cylindrical object in the path of a uniform gas stream is such that the total pressure of the gas stream exists on the upstream face of the cylinder and the flow separates and forms into eddies and swirls adjacent the downstream face of the cylinder. The shield 33 utilizes this flow pattern by presenting the narrow slot 34 on the upstream face of the shield 33 to the total pressure of the air stream so that a small portion of the stream enters the slot 34 and passes over the heater element 32, and by presenting the wide aperture 35 on 3 the downstream side of the shield 33 to the eddies and swirls formed there so that additional air is carried into the region of heating element 32. The general overall movement of the air is still downstream.

When the fuel is introduced into the main combustion chamber 12 and into the igniter 16', some atomization and vaporization take place due to the contact of the fuel with the air. The passage of most of the fuel-bearing air in the igniter tube 16 past the shield 33 which is heated by the heating element 32 serves tovaporize additional fuel, and the swirls and eddieson the downstream side of the shield 33' further atomize and vaporize fuel. The portion of the air entering the slot 34v on the up stream side of the shield 33 carries some fuel directly across the heating element'32 which ignites that portion of the mixture. The turbulent air on the downstream side of the shield 33 carries more fuel through the aperture 35 into the region'of the ignited mixture'whi'ch passed through the slot'34, and with the shield" 33' and the heater element 32 acting as'anchors, the flame moves downstream and into the combustion chamber'12i Since the heater element 32 is shielded from most of" the gas flow which passes around the shield 33, the heat loss prior'to ignition is low, so that the heater element 32 does not have to be operated at excessive temperatures to effect ignition. After the mixture has been ignited, the heater element 32 continues to radiate to a comparatively cool shield around a substantial portion of its periphery; This enables the heater element 32 to survive in a flame that would melt an ordinary unshielded plug.

The temperature of the'heater element is stabilized by the action of the shield 33, and the heating of the shield 33 by the heater element 32 accelerates vaporization of the fuel without unduly loading the plug 22', providing vaporized fuel for rapid ignition even when the initial temperature of the fuel entering the igniter tube 16 is low.

The shield 33 and plug 22 of this invention provide reliable ignition in the igniter tubes of gas turbines and jet engines. Because the shield aids in the vaporization of the fuel and the protection of the heater'element, the ignition of the igniter fuel is dependable and -rapid,- and the fuel in the combustion chamber is ignited before the chamber-is flooded with raw fuel.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

In combination, combustion apparatus comprising a conduit forming. an elongated chamber having supply means for directing a primary combustible mixture in a stream axially therethrough and an igniter for the combustion chamber comprising atube having one end portion extending through a side wall of the combustion chamber to be in communication with the primary combustible mixture stream and its other end portion disposed exteriorly of the combustion chamber, means in said other end portion of the igniter tube for supplying an independent combustible mixture thereto, a heater element within said igniter tube between saidlast named means and the combustion chamber, a tubular shield extending transversely of the igniter tube and enclosing the heater element, a narrow longitudinal slot in said shield providing an inlet to the shield for the independent combustible mixture during its passage through the igniter tube, a second slot in said shield disposed parallel to and diametrically opposite the first mentioned slot and being of substantially greater width than said first mentioned slot'whereby a portion of the independent combustible mixture enters the first mentioned slot and is directly ignited by the heater element while ,a portion of said mixture passes around the shield andthrough the second slot to be combusted and the resulting flame is anchored on theigniter structure to be directed into the combustion chamber by the continuing flow of -combustible mixture through the igniter. tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,670,819 Morris et a1 May 22', 1928 2,175,812 Meyerhoefer Oct. 10, 1939 2,261,458.. Bailey et a1. Nov. 4, 1941 2,632,300 Brzozowski Mar. 24, I953 

